The Impact of Modeling Errors on Interferometer Calibration for 21 cm Power Spectra

Ewall-Wice, Aaron; Dillon, Joshua S.; Liu, Adrian; Hewitt, Jacqueline

doi:10.48550/arxiv.1610.02689

Cited by 3 publications

(4 citation statements)

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“…If we take as a worst-case, the foreground precision requirement to be 10,000:1, then our target precision is 0.01%, while our current best demonstrated absolute accuracy is ∼1% but gets to 100% in the sidelobes. An error propagation study by Ewall-Wice et al (2016b) suggests that a flat 1% (0.04 dB) precision of the HERA beam provides sufficient suppression of foreground residuals to enable detection of most power spectrum modes outside the wedge. In a similar study, Shaw et al (2015) have set a requirement to know the CHIME to beamwidth to 0.1%, which for a Gaussian beam translates to ∼1dB error bars at a −40dB level.…”

Section: Overall Performancementioning

confidence: 99%

“…A similar error propagation study suggests that an accuracy of 1% across the beam will substantially reduce foreground bias for HERA and that other telescopes like SKA might require even better side-lobe beam accuracy (Ewall-Wice et al 2016b). Interpreting these requirements into a requirement on systematic error in the beam map, we assume that the multiplicative errors will, as is common for gain errors, have log-normal distribution.…”

Section: Introductionmentioning

confidence: 99%

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First Demonstration of ECHO: an External Calibrator for Hydrogen Observatories

Jacobs

Burba

Bowman

et al. 2017

PASP

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Multiple instruments are pursuing constraints on dark energy, observing reionization and opening a window on the dark ages through the detection and characterization of the 21cm hydrogen line for redshifts ranging from ∼1 to 25. These instruments, including CHIME in the sub-meter and HERA in the meter bands, are wide-field arrays with multiple-degree beams, typically operating in transit mode. Accurate knowledge of their primary beams is critical for separation of bright foregrounds from the desired cosmological signals, but difficult to achieve through astronomical observations alone. Previous beam calibration work at low frequencies has focused on model verification and does not address the need of 21cm experiments for routine beam mapping, to the horizon, of the as-built array. We describe the design and methodology of a drone-mounted calibrator, the External Calibrator for Hydrogen Observatories (ECHO), that aims to address this need. We report on a first set of trials to calibrate lowfrequency dipoles at 137MHz and compare ECHO measurements to an established beam-mapping system based on transmissions from the Orbcomm satellite constellation. We create beam maps of two dipoles at a 9°resolution and find sample noise ranging from 1% at the zenith to 100% in the far sidelobes. Assuming this sample noise represents the error in the measurement, the higher end of this range is not yet consistent with the desired requirement but is an improvement on Orbcomm. The overall performance of ECHO suggests that the desired precision and angular coverage is achievable in practice with modest improvements. We identify the main sources of systematic error and uncertainty in our measurements and describe the steps needed to overcome them.

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Section: Overall Performancementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

First Demonstration of ECHO: an External Calibrator for Hydrogen Observatories

Jacobs

Burba

Bowman

et al. 2017

PASP

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“…In addition to ba-sic signal-to-noise requirements demanding thousands of hours of observing time, the experiments must deal with the so-called "foregrounds" (which are essentially all other sources of radio emission) that can potentially eliminate a power spectrum detection or bias a measurement. Strategies to understand and correct for the effects of foregrounds, including how foregrounds interact with the instrument response, are the subject of many investigations (Morales et al 2006;Jelić et al 2008Jelić et al , 2010Bernardi et al 2009;Chapman et al 2012;Trott et al 2012;Morales et al 2012;Vedantham et al 2012;Thyagarajan et al 2015;Ewall-Wice et al 2016;Barry et al 2016;Trott & Wayth 2016;Patil et al 2016). Nevertheless, the bright foreground sources (such as diffuse Galactic radio emission and extragalactic radio galaxies and quasars) are spectrally smooth (Di Matteo et al 2002;Dillon et al 2014;Parsons et al 2014;Zaldarriaga et al 2004;Offringa et al 2016) which, in principle, confines the signal from these sources to the lowest-order (slowest varying) terms in the 1/frequency dimension of a power spectrum.…”

Section: Introductionmentioning

confidence: 99%

A High-Resolution Foreground Model for the MWA EoR1 Field: Model and Implications for EoR Power Spectrum Analysis

Procopio

Wayth

Line

et al. 2017

Publ. Astron. Soc. Aust.

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The current generation of experiments aiming to detect the neutral hydrogen signal from the Epoch of Reionisation (EoR) is likely to be limited by systematic effects associated with removing foreground sources from target fields. In this paper we develop a model for the compact foreground sources in one of the target fields of the MWA's EoR key science experiment: the 'EoR1' field. The model is based on both the MWA's GLEAM survey and GMRT 150 MHz data from the TGSS survey, the latter providing higher angular resolution and better astrometric accuracy for compact sources than is available from the MWA alone. The model contains 5049 sources, some of which have complicated morphology in MWA data, Fornax A being the most complex. The higher resolution data show that 13% of sources that appear point-like to the MWA have complicated morphology such as double and quad structure, with a typical separation of 33 arcsec. We derive an analytic expression for the error introduced into the EoR two-dimensional power spectrum due to peeling close double sources as single point sources and show that for the measured source properties, the error in the power spectrum is confined to high k ⊥ modes that do not affect the overall result for the large-scale cosmological signal of interest. The brightest ten mis-modelled sources in the field contribute 90% of the power bias in the data, suggesting that it is most critical to improve the models of the brightest sources. With this hybrid model we reprocess data from the EoR1 field and show a maximum of 8% improved calibration accuracy and a factor of two reduction in residual power in k-space from peeling these sources. Implications for future EoR experiments including the SKA are discussed in relation to the improvements obtained.

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“…Work by Barry et al (2016) to simulate the effects of antenna cable reflections in the MWA signal chain demonstrated the requirement for smoothness across the bandpass. More recently, Offringa et al (2016) and Ewall-Wice et al (2016) studied the impact of calibration errors due to unmodelled foreground sources, and found that residual source chromatic structure impedes the ability of instruments to perform EoR science. Relevant to this work, Trott & Wayth (2016) used an ideal estimator to quantify the tolerances on smoothness of the intrinsic SKA-Low bandpass response required for the proposed EoR/CD experiments to be undertaken successfully.…”

Section: Introductionmentioning

confidence: 99%

Spectral performance of Square Kilometre Array Antennas – II. Calibration performance

Trott

Acedo

Wayth

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We test the bandpass smoothness performance of two prototype Square Kilometre Array (SKA) SKA1-Low log-periodic dipole antennas, the SKALA2 and SKALA3 ('SKA Log-periodic Antenna'), and the current dipole from the Murchison Widefield Array (MWA) precursor telescope. Throughout this paper, we refer to the output complex-valued voltage response of an antenna when connected to a low noise amplifier (LNA), as the dipole bandpass. In Paper I (de Lera Acedo et al. 2017), the bandpass spectral response of the log-periodic antenna being developed for the SKA1-Low was estimated using numerical electromagnetic simulations and analyzed using low-order polynomial fittings and it was compared with the HERA antenna against the delay spectrum metric. In this work, realistic simulations of the SKA1-Low instrument, including frequency-dependent primary beam shapes and array configuration, are used with a weighted least-squares polynomial estimator to assess the ability of a given prototype antenna to perform the SKA Epoch of Reionisation (EoR) statistical experiments. This work complements the ideal estimator tolerances computed for the proposed EoR science experiments in Trott & Wayth (2016), with the realised performance of an optimal and standard estimation (calibration) procedure. With a sufficient sky calibration model at higher frequencies, all antennas have bandpasses that are sufficiently smooth to meet the tolerances described in Trott & Wayth (2016) to perform the EoR statistical experiments, and these are primarily limited by an adequate sky calibration model, and the thermal noise level in the calibration data. At frequencies of the Cosmic Dawn (CD), which is of principal interest to SKA as one of the first next-generation telescopes capable of accessing higher redshifts, the MWA dipole and SKALA3 antenna have adequate performance, while the SKALA2 design will impede the ability to explore this era.

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The Impact of Modeling Errors on Interferometer Calibration for 21 cm Power Spectra

Cited by 3 publications

References 0 publications

First Demonstration of ECHO: an External Calibrator for Hydrogen Observatories

First Demonstration of ECHO: an External Calibrator for Hydrogen Observatories

A High-Resolution Foreground Model for the MWA EoR1 Field: Model and Implications for EoR Power Spectrum Analysis

Spectral performance of Square Kilometre Array Antennas – II. Calibration performance

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